Formation of normal cells, tissues and organs in the body is achieved through expression of genes at appropriate times, in appropriate places and in appropriate quantities. As a result, normal function is exerted. For example, neural genes must be expressed properly in neuronal cells but not in non-neural cells. NRSE/RE1 (neural restrictive silencer element/repressor element 1) is a silencer consisting of 21 base pairs and present in the vicinity of neuron specific genes. This silencer plays a central role in neuron-specific transcriptional regulation of more than 30 genes for such substances as neurotransmitter synthetases, ion channels, neuronal growth-associated proteins, and so forth. It is said that approximately 1000 genes (mainly neuron specific genes) have this silencer. This silencer does not work in neuronal cells but suppresses expression of neuron specific genes in non-neuronal cells, to thereby assure expression of neuron specific genes in neuronal cells. It is also believed that this silencer is not only involved in the expression control of neuron specific genes but also involved in terminal differentiation of neuronal cells. It is NRSF/REST (neural restrictive silencer factor) that has been identified as a transcriptional repression factor which binds to the above-described NRSE/RE1 and represses expression of neuron specific genes in non-neuronal cells.
It is reported that abnormal expression of NRSF/REST and genes targeted by NRSF/REST is involved in neurodegenerative diseases, such as Down's syndrome, Alzheimer's disease and Huntington's disease, and medulloblastoma.
Down's syndrome is a disease caused by chromosome 21 trisomy mutation. Examination of difference in genes between neural tissues of fetuses dying from Down's syndrome and those of normal fetuses revealed that expression of SCG10 (a neuron-specific growth-associated protein) gene and other genes targeted by NRSF/REST such as decreased greatly in the former. On the other hand, those proteins regulated by transcription factors other than NRSF/REST were expressed normally (Non-Patent Document No. 1).
Alzheimer's disease is a disease caused by accumulation of β amyloid and neurofibrillary tangle and neuronal death. Expression of SCG10 was altered in Alzheimer's disease brains (Non-Patent Document No. 2).
Medulloblastoma is the most malignant brain tumor in children. Expression levels of NRSF/REST in medulloblastoma cells are very high. A recombinant protein REST-VP16 that antagonizes NRSF/REST and activates genes there targeted thereby promotes expression of neuronal genes and also activates the caspase cascade to thereby induce apoptosis. REST-VP16 is a potential therapeutic (Non-Patent Document No. 3).
Huntington's disease is a progressive, neurodegenerative disease manifesting choreic movement, dementia and personality change as major symptoms. It is believed that abnormal huntingtin molecules with a repeat structure of glutamine residues form aggregates to thereby induce neurodegeneration. Wild-type huntingtin binds to NRSF/REST in the cytoplasm to regulate the binding of NRSF/REST to NRSE/RE1. On the other hand, this control is lost in Huntington's disease; thus, neuronal genes are not expressed sufficiently (Non-Patent Document No. 4).
Chronic pain caused by neuronal disorders (neuropathic pain) presents complicated pain symptoms in which positive symptoms (pain hypersensitivity and allodynia (a strong pain induced by a tactile stimulus)) and negative symptoms (hypoesthesia) are mixed. Since this abnormal pain shows resistance to anti-inflammatory drugs and morphine, it is regarded as intractable pain.
Recently, Uchida et al. revealed that expression of the silencer factor NRSF/REST is enhanced in primary sensory neurons after neuropathy to silence a group of pain-associated genes (Nav1.8, MOP, TRPM8, TRPA1 and Kv4.3) through epigenetic modification (lowering of histone acetylation) and induce C-fiber hypoesthesia and morphine resistance which are characteristic of neuropathic pain (Non-Patent Documents Nos. 7, 8, 9 and 10).
Further, Naruse et al. revealed that the N-terminal transcriptional repressor domain of NRSF/REST recruits HDAC through co-repressor mSin3 and that the C-terminal transcriptional repressor domain recruits HDAC through CoREST, and suggested that NRSF/REST represses transcription by deactivation of the chromatin structure (Non-Patent Document No. 5).
The present inventors have already analyzed the structure of a complex composed of the N-terminal transcription repressor domain of NRSF (associated with Huntington's disease, medulloblastoma and neuropathic pain) and the PAH1 domain of co-repressor mSin3B which specifically binds to that domain (Patent Document No. 1 and Non-Patent Document No. 6).
However, no compounds have been reported so far which bind to mSin3B that specifically binds to neural restrictive silencer factor NRSF.